The over production of acid in an animal by microorganisms can cause acidosis which is defined as a condition of pathologically high acidity of the blood. In ruminants the term is expanded to include acidic conditions in the rumen.
Acidosis in ruminants is a frequently observed acute condition that is also known as "grain engorgement", "grain overload" or "acute indigestion". It occurs when the diet of ruminants is changed abruptly to contain large amounts of starch or other rapidly fermentable carbohydrates. A high incidence of acidosis is associated with feed lot livestock when their diet is rapidly changed from a forage-based ration to a grain-based ration. The rumnen undergoes a marked decrease of pH initiated by an increased rate of production of acids during the fermentative digestion of grains. The acids are then absorbed into the blood stream resulting in many of the clinical symptoms of acidosis. In many instances, Streptococcus bovis becomes the dominant bacteria as pH drops resulting in the production of lactic acid which is then absorbed from the rumen. The growth and metabolic activity of this and other acid producing organisms further lowers rumen pH. The condition of acidosis can be acute, posing a life-threatening situation, or chronic (sub-acute), resulting in reduced feed intake and weight gain.
Gross symptoms of acidosis include reduction or cessation of feed consumption (anorexia), loose faeces or diarrhoea, a listless, depressed or distressed appearance, founder or sore feet and death. Other symptoms that can be measured or observed after the onset of acidosis include decreased rate of grain and feed efficiency, high incidence of abscessed livers at slaughter, ruminates in slaughtered or dead animals, altered blood metabolic profile and incidence of polioencephalomalacia. Abscessed livers are condemned at slaughter, are an economic loss to the meat processor and ultimately adversely affect the market price of livestock. In particular, cattle with badly abscessed livers do not gain weight as rapidly or efficiently as unaffected animals.
Non-ruminant animals such as horses and the like are also susceptible to acidosis. The increasing popularity of horse related sports and activities has also led to an increase in the total incidence of acidosis in these animals. Horses are often housed in close quarters and are routinely grain fed when other fodder is unavailable, leading to the increased risk of acidosis.
In order to minimise or prevent the incidence of acidosis in livestock, current practices centre around management techniques, including introducing grain slowly to the diet of the animals. This involves close monitoring of daily feed intake, checking the animals condition and providing fresh feed and water daily. This method is time-consuming as rations must be mixed and prepared and the animals must be monitored carefully for the incidence of acidosis.
Recent studies have demonstrated that inclusion of antibiotics including Virginiamycin in the diet removes the need for a gradual introduction to grain feeding in feedlot animals or animals fed on grain in a drought. The inclusion of antibiotics also reduces the possibility of animal losses. The widespread use of antibiotics in the livestock industry however is not considered acceptable as the potential for emergence of drug-resistant microbial strains is high. In addition, there is an attendant risk to public health through antibiotic residues in animal products. The presence of antibiotics in animal products may also endanger export earnings as many countries prohibit the importation of animal products containing antibiotics.
Another strategy to reduce the incidence of abscessed livers and the effects of acidosis is to include dietary buffers or neutrlisers (bicarbonates, hydroxides, silicates) in feed. These additives have beneficial effects during initial phase of adaptation to high carbohydrate containing diets during the first few weeks of feeding. These additives do not, however, provide consistent benefit in feedlot performance over the entire finishing period. The levels used, that are initially beneficial, may cause overall performance to be inferior to that obtained without additives.
Acidosis can also be a major problem during drought conditions where grain is often the only food source available for livestock. To place animals on a pure grain diet under these harsh conditions can cause a high incidence of acidosis often leading to death. There is a real need to have an economical and efficient means of protecting animals from the incidence of the over production of acid and acidosis.
The present inventors have developed an alternative strategy for the prevention of the over production of acid and acidosis in animals.